This invention relates to a D.C. motor, and more particularly relates to an improvement for sustaining torque when the motor is de-energized.
Referring now to FIG. 6, one example of a conventional D.C. motor 50 is explained. This conventional motor 50 includes four magnetic poles 52 for establishing a field magnet and an armature core 53. The armature core 53 further includes spindle 53a and five teeth 53b which project spokewise from the spindle 53a and face the magnetic poles 52.
This type of motor is utilized as an actuator as shown in FIG. 7. When the D.C. motor 50 is energized, the motor 50 stores energy in a torque storage mechanism 63 via a worm gear 61 and worm wheel 62. The torque storage mechanism 63 could be a spiral spring or the like. The stored energy is converted into liner movement by a rack 66 and a pinion 67 via reduction gears 64 and 65. The amount of stored energy is detected by an angle detector 68. The angle detector 68 de-energizes the motor 50 if the angle detector 68 detects a predetermined angular movement of the worm wheel 62. When the motor 50 is de-energized, the stored energy in the storage mechanism is transmitted to the motor 50 via the worm gear 61 and the worm wheel 62 and may cause the motor 50 to reverse. Therefore, the motor 50 has to have a minimum sustaining torque against the reaction of the torque storage mechanism 63.
However, only one tooth among the five teeth 53b is located directly in front of a magnetic pole 52 of the field magnet in the typical conventional D.C. motor 50 shown in FIG. 6. The other teeth 53b which are not directly in front of the magnetic poles 52 do not contribute to the sustaining torque sufficiently. Accordingly, the conventional D.C. motor does not have enough sustaining torque for overcoming the reaction of the storage mechanism 63.